The invention relates to a refrigerator having a cold producer including at least one pneumatically operated displacer movable in a cylindrical chamber, and having an apparatus which serves for controlling the delivery of the working gas to the cylindrical chamber and the delivery of the gas necessary for the pneumatic operation of the displacer, plus a compressor for the gas supply.
Refrigerators are cryogenerators or low-temperature producing machines in which a thermodynamic cyclical process takes place (cf. U.S. Pat. No. 2,906,101, for example). One type of single-stage refrigerator is, essentially, a cylindrical chamber containing a reciprocating displacer. The chamber is connected alternately, in a certain manner, to a high-pressure gas reservoir and a low-pressure gas reservoir, so that the thermodynamic cyclical process (Stirling process, Gifford-McMahon process, etc.) takes place during the reciprocating movement of the displacer. The result is that heat is removed from one of the two ends of the chamber toward and away from which the displacer reciprocates. Temperatures down to less than 10K can be produced with two-stage refrigerators of this kind using helium as the working gas.
It is known, (cf. German Offenlegungsschrift Nos. 1,426,975, 1,501,049 and 2,051,203) to drive the displacer pneumatically and to use the working gas itself as the gas producing the pneumatic operation. In the refrigerators of German Offenlegungsschrift Nos. 1,426,975 and 1,501,049, the displacer is equipped with a driving piston the cylinder for which is connected by a gas control system to the high pressure or low pressure gas reservoir at the moment that is correct for the operation of the cyclical process. The gas control system serves furthermore for letting the working gas out of and into the cylinder of the displacer. In the subject matter of Offenlegungsschrift No. 2,051,203, a valve system additionally supplies a chamber with a volume of buffer gas. This chamber communicates with the hot end of the working cylinder through a throttle and has the effect of a pneumatic drive for operating the displacer.
In the actual (non-schematic) embodiments, shown in the above references the cold producer, i.e., the working cylinder with the displacer, forms with the gas control system (valve system or valve control rotor with drive) a single unit for which the expression "cold head" has become established. In order to put such a cold head in operation, it has to be connected to a suitable compressor through a low-pressure and a high-pressure line supplying the working gas. Additionally, an electrical connection must be made for the power supply of the valve control system or of an electric motor operating the valve control rotor. The connecting lines between the cold head and the compressor or power supply can be relatively long, so that for certain applications it is possible to set up the relatively small cold heat at a great distance from the supply apparatus. The small size of the unit producing the cold and the ease of making the connection between the cold head and its supply system are the important advantages of refrigerators over low-temperature apparatus operating with liquid refrigerants (bath cryostats and bath cryopumps or evaporator cryostats and evaporator cryopumps).